Chair with a pivoting backrest

ABSTRACT

A chair having a fixed support structure including two side uprights, a backrest having two side portions, and a pair of elastic joints connecting said side portions of the backrest to said side uprights, wherein each of said elastic joints comprises: a bushing fixed to a respective side upright, a helical spring having a longitudinal axis, the helical spring having an upper end resting against a front wall of the bushing, a compression member resting against a lower end of the spring, an upper attachment fixed to a corresponding side portion of the backrest, and a rigid connecting rod having an upper end and a lower end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Italian patent application numberTO2013A000650, filed Jul. 31, 2013, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chair with a pivoting backrestcapable of tilting backwards under a thrust applied by the user's back.

2. Description of Prior Art

In the state of the art, there are various known solutions of chairs inwhich the backrest is connected to a fixed support structure by a pairof elastic joints, each of which comprises an upper support insertedinto a tubular portion of the backrest, a lower support inserted into atubular element of the fixed support structure and an elastic element,which allows an inclination between the upper support and the lowersupport.

For example, the document EP2183997 of the same applicant describes achair comprising a base structure including two rear tubular elements, abackrest having two tubular portions and two elastic devices, each ofwhich has an upper support inserted into a tubular portion of thebackrest, a lower support inserted into the corresponding tubularelement of the base structure and an elastic element deformable bybending to allow pivoting between the upper support and the lowersupport, wherein each of the elastic devices comprises a plurality ofstacked sectors, arranged between the upper support and the lowersupport.

The elastic elements that are deformable by bending have the drawback ofa limited elastic force for opposing the backward thrust applied by theuser.

In principle, with elastic elements in compression formed, for example,by helical compression springs, it would be possible to increase theforce provided by the elastic joints that contrast the backward thrustapplied by the user on the backrest of the chair. However, with helicalcompression springs arranged coaxially to the side uprights of thebackrest, the lever arm for the compression of the springs is limited.

SUMMARY OF THE INVENTION

The present invention aims to provide a chair with a pivoting backrestequipped with simple and robust elastic joints, capable of providing ahigh elastic force that counteracts the backward thrust applied by theuser on the backrest of the chair.

According to the present invention, this object is achieved by a chairhaving the characteristics forming the subject of claim 1.

The claims form an integral part of the disclosure provided in relationto the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in detail with reference tothe accompanying drawings, given purely by way of non-limiting example,wherein:

FIG. 1 is a side view of a chair according to the present invention inthe rest position;

FIG. 2 is a side view corresponding to FIG. 1, illustrating the backrestin the backwardly-inclined position;

FIG. 3 is an axial section of the part indicated by the arrow III inFIG. 1 in the rest position;

FIG. 4 is an axial section analogous to FIG. 3 in the position ofmaximum backward-inclination; and

FIG. 5 is an exploded perspective view of certain components of theelastic joint indicated by the arrow III in FIG. 1.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, numeral 10 indicates a chair accordingto the present invention. The chair 10 comprises a fixed supportstructure 12 including a pair of front legs 14 and a pair of rear legs16. The front legs 14 and the rear legs 16 are connected together bymeans of upper connecting elements 18. A seat 20 is fixed to the upperconnecting elements 18 of the fixed support structure 12.

The fixed support structure 12 comprises two tubular side uprights 22extending upwards. The two side uprights 22 are fixed with respect tothe support structure 12. For example, the side uprights 22 can be fixedto the upper connecting elements 18.

The seat 10 comprises a backrest 24 pivotally connected to the fixedsupport structure 12. The backrest 24 comprises a backrest panel 26having an arcuate shape, and two side portions 28 located laterally onopposite sides with respect to the backrest panel 26. The side portions28 can be formed in a monolithic manner with the backrest panel 26. Theside portions 28 of the backrest 24 are connected to the respective sideuprights 22 of the fixed support structure 12 by means of respectiveelastic joints 30.

With reference to FIG. 5, each elastic joint 30 comprises a bushing 32having a cylindrical wall 34 having an open lower end and an upper endfitted with a front wall 36. The bushing 32 can be equipped with aprojecting appendage 38 that projects upwards from the front wall 36.

The elastic joint 30 comprises a helical spring 40 housed within thecylindrical wall 34 of the bushing 32. The helical spring 40 has alongitudinal axis A coaxial to the axis of the cylindrical wall 34 ofthe bushing 32. The helical spring 40 has an upper end 42 and a lowerend 44. The upper end 42 rests against the front wall 36 of the bushing32. The lower end 44 of the helical spring 40 rests on a compressionmember 46. In the illustrated example, the compression member 46comprises a body of plastic material 48 and a metal washer 50. The bodyof plastic material 48 has a cylindrical portion 52 that couples, in asliding manner, with the lower end of the bushing 32. At the bottom ofthe cylindrical portion 52, a radially-projecting shoulder 54 is formed.The body 48 of the compression member 46 has a through hole 56 with arectangular section. The washer 50 rests against a lower surface of thebody 48. The washer 50 has a through hole 58 with a rectangular sectionaligned with the hole 56 of the body 48. Preferably, the washer 50 has aconvex deformed portion 60 that couples with a corresponding concaveseat 62 formed on the lower surface of the body 48. The washer 50 has aconcave seat 64 on the surface opposite to the convex projection 60.

The elastic joint 30 comprises a rigid connecting rod 66 preferably madeof metal. The connecting rod 66 preferably has a rectangular crosssection. The connecting rod 66 has a lower end 68 and an upper end 70equipped with respective holes 72, 74, engaged by respective pins 76,78. The axes of the pins 76, 78, indicated with B and C, are parallel toeach other, and transverse relative to the axis A of the spring 40.

The elastic joint 30 comprises an upper attachment 80 having a shank 82,which is fixed into a hole formed at the lower end of the respectiveside portion 28 of the backrest 24. The upper attachment 80 has a groove84 into which the upper end 70 of the connecting rod 66 is inserted. Theupper attachment 80 has a transverse hole 86, through which the upperpin 78 is inserted, which connects the upper end 70 of the connectingrod 66 to the upper attachment 80, in an articulated manner.

The elastic joint 30 is preferably provided with a ring of plasticmaterial 88 fitted on the appendage 38 of the bushing 32. The ring 88has a lower front surface, which rests on the front surface 36 of thebushing 32, and an upper surface 90 against which a lower surface 92 ofthe upper attachment 80 rests. As is illustrated in FIGS. 3 and 4, theupper surface 90 of the ring 88 and the lower surface 92 of the upperattachment 80 may have respective projecting and receding profiles inorder to establish a shape coupling.

As is visible in FIGS. 3 and 4, the bushing 32 of each elastic joint 30is fixed, for example by hammering, to the upper end of thecorresponding tubular upright 22 of the fixed support structure 12.

The lower portion of the connecting rod 66 extends through the holes 56and 58 of the body 48 and of the washer 50 of the compression member 46.The first pin 76 connects the lower end 68 of the connecting rod 66 tothe compression member 46 in an articulated manner. The pin 76 is housedin the concave seat 64 of the washer 50. The central portion of theconnecting rod 66 included between the ends 68, 70 extends through thehelical spring 40 and through a through hole 94 formed in the upper partof the bushing 32.

The upper end 70 of the connecting rod 66 that projects above the ring88 is bent forwards. In this way, the articulation axis C, between theupper end 70 of the connecting rod 66 and the upper attachment member80, is moved forward by a distance d (FIG. 3) with respect to thelongitudinal axis A of the spring 40. The articulation axis B of thelower end 68 of the connecting rod 66 of the compression member 46 isessentially located on the longitudinal axis A of the spring 40.

The effect of the forward displacement of the axis C with respect to thelongitudinal axis A of the spring 40 is that of increasing, all otherconditions being equal, the elastic torque applied by the springs 40 tothe backrest 24. When a backward thrust is applied to the backrest 24 bythe user's back, the upper attachment 80 pivots backwards about afulcrum point, indicated with F in FIGS. 3 and 4. The fulcrum point F isdefined by the point of mutual rotation between the contact surfaces ofthe upper attachment 80 and the ring 88. The rotation of the upperattachment 80 about the fulcrum point F compresses the spring 40 bymeans of the connecting rod 66. The return elastic force of the spring40 has a lever arm of dimension d1, with respect to the pivot fulcrum F.The lever arm d1 is increased thanks to the forward displacement of thearticulation axis C. Consequently, at a constant axial force exerted bythe spring 40, thanks to the forward displacement of the articulationaxis C, a higher torque on the backrest 24 is achieved, whichcounteracts the backward thrust applied by the user.

In the position of maximum backward inclination of the backrest,illustrated in FIG. 4, the radial shoulder 54 of the compression member46 rest against the lower end of the bushing 32 and forms a stroke end,which prevents further backward inclination of the backrest.

To stiffen the fixing area between the side portions 28 of the backrest24 and the corresponding upper attachments 80, each elastic joint 30 maybe fitted with a stiffening pin 96 (FIGS. 3 and 4) having an upperportion driven into a hole 98 of the side portion 28 of the backrest 24,and a lower portion driven into a hole 100 of the respective upperattachment 80.

Each elastic joint 30 can also be fitted with an protective elasticelement 102 arranged coaxially around the contact area between the upperattachment 80 and the ring 88, in order to avoid pinching of garments orparts of the body between the contact surfaces of the upper attachment80 and the ring 88.

Of course, without prejudice to the principle of the invention, thedetails of construction and the embodiments may vary widely with respectto those described and illustrated without departing from the scope ofthe invention as defined by the following claims.

The invention claimed is:
 1. A chair comprising: a fixed supportstructure including two side uprights; a backrest having two sideportions; and a pair of elastic joints connecting said side portions ofthe backrest to said side uprights, wherein each of said elastic jointscomprises: a bushing fixed to a respective side upright; a helicalspring having a longitudinal axis, the helical spring having an upperend resting against a front wall of the bushing; a compression memberresting against a lower end of the spring; an upper attachment fixed toa corresponding side portion of the backrest; and a rigid connecting rodhaving an upper end and a lower end articulated, respectively, to theupper attachment and to the compression member about respective axesparallel to each other and transverse with respect to said longitudinalaxis, wherein the articulation axis between the upper end of theconnecting rod and the upper attachment of each elastic joint is spacedforward with respect to said longitudinal axis.
 2. A chair according toclaim 1, wherein each elastic joint comprises a ring of plastic materialplaced between said upper attachment and said bushing.
 3. A chairaccording to claim 2, wherein said ring and said upper attachment haverespective surfaces in contact with each other, and shaped in such a wayas to establish a shape coupling.
 4. A chair according to claim 2,wherein each of said elastic joints comprises a protective elasticelement fitted on an area of contact between said upper attachment andsaid ring.
 5. A chair according to claim 1, wherein said connecting rodhas an upper end portion bent forward and housed in a grove of saidupper attachment, the upper end of said connecting rod being articulatedto the upper attachment by means of a pin.